On 01/31/2013 01:20:39 PM, Alexander Graf wrote:
On 31.01.2013, at 20:05, Alexander Graf wrote:
>
> On 31.01.2013, at 19:54, Scott Wood wrote:
>
>> On 01/31/2013 12:52:41 PM, Alexander Graf wrote:
>>> On 31.01.2013, at 19:43, Scott Wood wrote:
>>>> On 01/31/2013 12:21:07 PM, Alexander Graf wrote:
>>>>> How about something like this? Then both targets at least suck
as much :).
>>>>
>>>> I'm not sure that should be the goal...
>>>>
>>>>> Thanks to e500mc's awful hardware design, we don't know who
sets the MSR_DE bit. Once we forced it onto the guest, we have no
change to know whether the guest also set it or not. We could only
guess.
>>>>
>>>> MSRP[DEP] can prevent the guest from modifying MSR[DE] -- but we
still need to set it in the first place.
>>>>
>>>> According to ISA V2.06B, the hypervisor should set DBCR0[EDM] to
let the guest know that the debug resources are not available, and
that "the value of MSR[DE] is not specified and not modifiable".
>>> So what would the guest do then to tell the hypervisor that it
actually wants to know about debug events?
>>
>> The guest is out of luck, just as if a JTAG were in use.
>
> Hrm.
>
> Can we somehow generalize this "out of luck" behavior?
>
> Every time we would set or clear an MSR bit in shadow_msr on
e500v2, we would instead set or clear it in the real MSR. That way
only e500mc is out of luck, but the code would still be shared.
I don't follow. e500v2 is just as out-of-luck. The mechanism simply
does not support sharing debug resources.
What do you mean by "the real MSR"? The real MSR is shadow_msr, and
MSR_DE must always be set there if the host is debugging the guest. As
for reflecting it into the guest MSR, we could, but I don't really see
the point. We're never going to actually send a debug exception to the
guest when the host owns the debug resources.
Speaking of naming issues, "guest_debug" is very ambiguous...
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 38a62ef..9bdb845 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -133,6 +133,29 @@ static void kvmppc_vcpu_sync_fpu(struct kvm_vcpu
*vcpu)
#endif
}
+static void kvmppc_vcpu_sync_debug(struct kvm_vcpu *vcpu)
+{
+ u32 is_debug = vcpu->arch.shared->msr & MSR_DE;
+
+ /* Force debug to on in guest space when user space wants to
debug */
+ if (vcpu->guest_debug)
+ is_debug = MSR_DE;
+
+#ifdef CONFIG_KVM_BOOKE_HV
+ /*
+ * Since there is no shadow MSR, sync MSR_DE into the guest
+ * visible MSR.
+ */
+ vcpu->arch.shared->msr &= ~MSR_DE;
+ vcpu->arch.shared->msr |= is_debug;
+#endif
+
+#ifndef CONFIG_KVM_BOOKE_HV
+ vcpu->arch.shadow_msr &= ~MSR_DE;
+ vcpu->arch.shadow_msr |= is_debug;
+#endif
+}
The "&= ~MSR_DE" line is pointless on bookehv, and makes it harder to
read. I had to stare at it a while before noticing that you initially
set is_debug from the guest MSR and that you'd never really clear
MSR_DE here on bookehv.
-Scott
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